Preparation And Application Of Sodium Alginate/Nanocellulose Composite Cryogels By Freezing Induction By Oxa-Michael Reaction

Natural polysaccharide-based monolithic cryogels have been widely used in many fields such as water purification,cell separation,catalysis,biotechnology,bioremediation,and biosensor ascribing to their environment-friendliness,multiple functionality,easy availability,and low cost.Cryogels are 3D materials with a macroporous structure,using solvent ice crystals as pore-forming agents at low temperatures,they are able to address some of the limitations of hydrogels.In this paper,by compounding sodium alginate（SA）and nanocellulose（MFC and CNF-C）to solve the poor stability and water resistance of SA and low removal ability of original cellulose nanofibers were simultaneously solved,the prepared monoliths are suitable for different application scenarios.This work tries to avoid the use of toxic organic reagents,proposed the experimental process the concept of green chemistry.To the best of our information,this is the first study of polysaccharide-based cryogel fabrication using the freeze-activated oxa-Michael reaction.The main details of the dissertation are as follows:In this study,we present a novel freezing-induced chemical crosslinking strategy to develop a shapeable and underwater super-elastic polysaccharide-based monolithic cryogels with interconnected macropores using SA and Microfibrillated cellulose（MFC）at-12°C,and also to investigate the mechanism of activating the chemical reaction during the freeze step.Cryogels was prepared using MFC and SA（M/G=1:1）as building block and divinyl sulfone（DVS）as cross-linker.Due to high aspect ratio and fiber entanglements,MFC was usually utilized to fabricate the composite cryogels with the reinforcement effect.The fabricated cryogels is rich in carboxyl groups,and exhibits the three-dimensional（3D）wall perforated cellular structure under SEM.As analyzed by mercuryintrusion porosimetry,the MFC/SA cryogel presented the macropores with the mean size range of 10 to 50μm,which ensures non-clarified and viscous feed-streams pass smoothly.Using lysozyme as template protein,the MFC/SA cryogels reveal a high lysozyme adsorption capacity of 294.12mg/g,exceeding most of absorbent materials previously reported.MFC/SA cryogel-packed column can continuously adsorb and purify lysozyme from egg white,and the extraction capacity is retained after 6 cycles.Furthermore,carboxylated cellulose nanofiber（CNF-C）was introduced into the MFC and SA systems,the intermolecular hydrogen bonds promoted the parallel stacking of multiple cellulose chains,and the intrachain and interchain hydrogen bond networks made the cellulose polymer more stable and the system more uniform.Alginate-based cryogel adsorbents for cisplatin removal were prepared by freezing-induced Oxa-Michael reaction.The adsorption test showed that high cisplatin uptake ability could be achieved to recorded to be 353.99 mg/g maximumly.It was also observed that loading the cryogel into a syringe as a packed column simulates the actual treatment of wastewater,allowing continuously adsorb cisplatin from wastewater（up to 2500 m L per gram of cryogel）.In addition,the SA/MFC/CNF cryogel adsorbent exhibited good regeneration（Na OH）,recyclability（more than 6times）,and stability（60 days）.According to the investigation,there are a few reports on the removal of the toxic cisplatin using gels.We also observed that the continuous adsorption of cisplatin under dynamic conditions has also not been studied.It is important to understand the cisplatin-adsorption process and mechanism to effectively use the fabricated gels to remove cisplatin from contaminated water bodies.Since SA/MFC/CNF cryogels are superhydrophilic in air,the prepared SA/MFC/CNF-Mⁿ⁺cryogels were post-treated with metal cation solutions(Mⁿ⁺=Na⁺,Ca²⁺and Fe³⁺).cryogels has superhydrophilic/underwater oleophobicity and can be used not only for pure oil/water separation,but also for the successful separation of surfactant-stabilized oil/water emulsions.The above three cryogels(MFC/SA,SA/MFC/CNF,and SA/MFC/CNF-Mⁿ⁺)all use a low-cost atmospheric drying method,following the process of acetone-solvent exchange,was followed instead of the energy-intensive freeze-drying and supercritical drying methods to fabricate the cryogels.These samples do not collapse and shrink significantly after acetone evaporation,and exhibit excellent mechanical strength in air.The interconnected pores could allow the free entry and exit of water during the deformation process,imparting the reversible deformation characteristics to the three cryogels.The stress-strain curve results obtained through the underwater cyclic compression performance test show that the cryogels can withstand more than80%of the strain applied and compress 200 times without any breakage,proving that the prepared cryogels have excellent elasticity,underwater shape recovery,excellent fatigue resistance and structural stability.